U.S. patent number 6,686,990 [Application Number 09/725,912] was granted by the patent office on 2004-02-03 for scanning exposure method with reduced time between scans.
This patent grant is currently assigned to Nikon Corporation, Inc.. Invention is credited to Andrew J. Hazelton, Bausan Yuan.
United States Patent |
6,686,990 |
Hazelton , et al. |
February 3, 2004 |
Scanning exposure method with reduced time between scans
Abstract
A positioning method in which a system performs operations
relative to areas on a substrate by a series of relative movements
between the system and substrate scanning exposures. The method
includes the steps of disposing a first area relative to a system
performing an operation relative to the first area, and moving the
substrate from a first position where the first operation relative
to the first area has finished to a second position where a second
operation relative to a second area is to start, and synchronously
moving the system from a third position where the first operation
relative to the first area has finished to a fourth position where
the second operation relative to the second area is to start. An
acceleration of the substrate during movement from the first
position to the second position and an acceleration of the system
during movement from the third position to the fourth position
continually have absolute values greater than zero.
Inventors: |
Hazelton; Andrew J. (San
Carlos, CA), Yuan; Bausan (San Jose, CA) |
Assignee: |
Nikon Corporation, Inc. (Tokyo,
JP)
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Family
ID: |
23218754 |
Appl.
No.: |
09/725,912 |
Filed: |
November 30, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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314146 |
May 19, 1999 |
6285438 |
Sep 4, 2001 |
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Current U.S.
Class: |
355/53;
355/77 |
Current CPC
Class: |
G03F
7/70358 (20130101); G03F 7/70725 (20130101) |
Current International
Class: |
G03F
7/20 (20060101); G03B 027/42 (); G03B 027/32 () |
Field of
Search: |
;355/52,53,55,67-71,77
;356/399-401 ;250/548 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 785 571 |
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Jul 1997 |
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EP |
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01-260510 |
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Oct 1989 |
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JP |
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7-161614 |
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Jun 1995 |
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JP |
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08-249073 |
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Sep 1996 |
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JP |
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Primary Examiner: Nguyen; Henry Hung
Attorney, Agent or Firm: Finnegan, Henderson, Farabow,
Garrett & Dunner, L.L.P.
Parent Case Text
This is a continuation of application Ser. No. 09/314,146, filed
May 19, 1999, now U.S. Pat. No. 6,285,438, issued Sep. 4, 2001,
which is incorporated herein by reference.
Claims
What is claimed is:
1. A step-and-scan exposure method comprising the steps of:
disposing a first shot area of a substrate under a projection
optical system; exposing a first pattern onto the first shot area
through the projection optical system; and moving the substrate
from a first position where the exposure of the first pattern onto
the first shot area has finished to a second position where the
exposure of a second pattern onto a second shot area is to start,
wherein an acceleration of the substrate during movement from the
first position to the second position continually has an absolute
value greater than zero and no pattern is exposed onto the
substrate during movement from the first position to the second
position.
2. The step-and-scan exposure method according to claim 1, wherein
the substrate moves in a first direction during exposure of the
first pattern and the substrate moves in a second opposite
direction during exposure of the second pattern.
3. The step-and-scan exposure method according to claim 1, wherein
the exposure step further comprises: moving the substrate at a
first constant velocity during exposure of the first pattern onto
the first shot area.
4. The step-and-scan exposure method according to claim 1, wherein
the acceleration of the substrate during movement from the first
position to the second position includes a deceleration stage and
an acceleration stage, wherein an absolute value of a velocity of
the substrate reduces to zero during the deceleration stage and
increases from zero during the acceleration stage.
5. The step-and-scan exposure method according to claim 1, wherein
an absolute value of a rate of change of the acceleration is
substantially constant.
6. The step-and-scan exposure method according to claim 1, wherein
the acceleration remains substantially constant during a portion of
the movement of the substrate from the first position to the second
position.
7. A step-and-scan exposure method in which patterns on a mask are
transferred to shot areas on a photosensitive substrate by a series
of scanning exposures, the method comprising the steps of:
disposing a first pattern above a projection optical system;
exposing the first pattern onto a first shot area through the
projection optical system; and moving the mask from a first
position where the exposure of the first pattern has finished to a
second position where the exposure of a second pattern onto a
second shot area is to start, wherein an acceleration of the mask
during movement from the first position to the second position
continually has an absolute value greater than zero and no pattern
is exposed onto the substrate during movement from the first
position to the second position.
8. The step-and-scan exposure method according to claim 7, wherein
the mask moves in a first direction during exposure of the first
pattern and the mask moves in a second opposite direction during
exposure of the second pattern.
9. The step-and-scan exposure method according to claim 7, wherein
the exposure step further comprises: moving the mask at a first
constant velocity during exposure of the first pattern onto the
first shot area.
10. The step-and-scan exposure method according to claim 7, wherein
the acceleration of the mask during movement from the first
position to the second position includes a deceleration stage and
an acceleration stage, wherein an absolute value of a velocity of
the mask reduces to zero during the deceleration stage and
increases from zero during the acceleration stage.
11. The step-and-scan exposure method according to claim 7, wherein
an absolute value of a rate of change of the acceleration is
substantially constant.
12. The step-and-scan exposure method according to claim 7, wherein
the acceleration remains substantially constant during a portion of
the movement of the mask from the first position to the second
position.
13. A step-and-scan exposure method in which patterns on a mask are
transferred to shot areas on a photosensitive substrate by a series
of scanning exposures, the method comprising the steps of:
disposing a first shot area under a projection optical system and a
first pattern above the projection optical system; exposing the
first pattern onto the first shot area through the projection
optical system; and moving the substrate from a first position
where the exposure of the first pattern onto the first shot area
has finished to a second position where the exposure of a second
pattern onto a second shot area is to start, and synchronously
moving the mask from a third position where exposure of the first
pattern onto the first shot area has finished to a fourth position
where exposure of the second pattern onto the second shot area is
to start, wherein an acceleration of the substrate during movement
from the first position to the second position and an acceleration
of the mask during movement from the third position to the fourth
position continually have absolute values greater than zero and no
pattern is exposed onto the substrate during movement from the
first position to the second position.
14. A method of moving a substrate comprising the steps of:
disposing a first area of the substrate under a system; performing
a first operation with respect to the first area; and moving the
substrate from a first position where the first operation with
respect to the first area has finished to a second position where a
second operation with respect to a second area is to start,
continually at an acceleration having an absolute value greater
than zero without performing any operation with respect to the
substrate.
15. The method according to claim 14, wherein the substrate moves
in a first direction during the first operation and the substrate
moves in a second opposite direction during the second
operation.
16. The method according to claim 14, wherein the performing step
further comprises: moving the substrate at a first constant
velocity during the first operation with respect to the first
area.
17. The method according to claim 14, wherein the acceleration of
the substrate during movement from the first position to the second
position includes a deceleration stage and an acceleration stage,
wherein an absolute value of a velocity of the substrate reduces to
zero during the deceleration stage and increases from zero during
the acceleration stage.
18. The method according to claim 14, wherein an absolute value of
a rate of change of the acceleration is substantially constant.
19. The method according to claim 14, wherein the acceleration
remains substantially constant during a portion of the movement of
the substrate from the first position to the second position.
20. A method of moving a system above a substrate in which
operations are performed relative to areas of the substrate,
comprising the steps of: disposing the system above a first area of
the substrate; performing a first operation with respect to the
first area; and moving the system from a first position where the
first operation has finished to a second position where a second
operation is to start, wherein an acceleration of the system during
movement from the first position to the second position continually
has an absolute value greater than zero and no operation with
respect to the substrate is performed during movement from the
first position to the second position.
21. The method of moving a system according to claim 20, wherein
the system moves in a first direction during the first operation
and the system moves in a second opposite direction during the
second operation.
22. The method of moving a system according to claim 20, wherein
the performing step further comprises: moving the system at a first
constant velocity during the first operation with respect to the
first area.
23. The method of moving a system according to claim 20, wherein
the acceleration of the system during movement from the first
position to the second position includes a deceleration stage and
an acceleration stage, wherein an absolute value of a velocity of
the system reduces to zero during the deceleration stage and
increases from zero during the acceleration stage.
24. The method of moving a system according to claim 23, wherein
the system moves in a first direction during the deceleration stage
and a second opposite direction during the acceleration stage.
25. The method of moving a system according to claim 20, wherein an
absolute value of a rate of change of the acceleration is
substantially constant.
26. The method of moving a system according to claim 20, wherein
the acceleration remains substantially constant during a portion of
the movement of the system from the first position to the second
position.
27. A method of moving a system and a substrate to perform a series
of operations, the method comprising the steps of: disposing a
first area of the substrate relative to the system; performing a
first operation with respect to the first area; and moving the
substrate from a first position where the first operation has
finished to a second position where a second operation is to start,
and synchronously moving the system from a third position where the
first operation with respect to the first area has finished to a
fourth position where the second operation with respect to the
second area is to start, wherein an acceleration of the substrate
during movement from the first position to the second position and
an acceleration of the system during movement from the third
position to the fourth position continually have absolute values
greater than zero and no operation with respect to the substrate is
performed during movement from the first position to the second
position.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a scanning exposure method of the
step-and-scan type in which a mask and a substrate are
synchronously scanned to transfer a mask pattern onto the
substrate. More specifically, the invention relates to such a
scanning exposure method in which the time between scans of the
pattern is reduced.
2. Discussion of the Related Art
In a photolithography process for manufacturing a semiconductor or
the like, a projection-type exposure apparatus uses a projection
optical system to transfer an image of a pattern on a mask or a
reticle to a photosensitive substrate. The substrate typically is a
wafer or glass plate with photoresist applied thereto. During the
process, a much larger pattern on the reticle is transferred to the
wafer. For example, a reticle pattern may be about four times the
size of the transferred image to the wafer. Various scanning-type
exposure apparatuses have been developed in which the reticle and
the wafer are scanned synchronously with respect to an illumination
area, often a slit-like illumination area, to transfer the large
pattern to the wafer.
More particularly, a wafer includes a plurality of shot areas or
chips on which a reticle pattern is scanned and exposed. After
scanning and exposing a reticle pattern onto a first shot area of a
wafer, the wafer and reticle must be stepped to the next shot area
and pattern, respectively, to begin the scanning of that next
pattern. The stepping of the wafer positions the subsequent shot
area to a scanning start position. Often, during the stepping of
the wafer, the direction of scanning must be reversed. The stepping
and scanning exposure is repeated for all shot areas on the wafer.
This system of repeating the stepping and the scanning exposure is
commonly called a step-and-scan system.
U.S. patent application Ser. No. 08/350,619, filed Dec. 7, 1994,
discloses a step-and-scan system, and is hereby incorporated by
reference. As shown at FIGS. 7(a), 7(b), and 7(c), the disclosed
system illustrates a velocity wave form having linear velocity
segments.
In the step-and-scan system, the stepping time between scans
represents an inefficiency in which no scanning occurs. This
inefficiency increases the total time to manufacture a chip on a
wafer and thereby limits the throughput of wafers in a production
process. The need therefore exists to minimize the stepping time
between scans to increase wafer throughput.
SUMMARY OF THE INVENTION
Objects and advantages of the invention will be set forth in part
in the description which follows, and in part will be obvious from
the description, or may be learned by practice of the invention.
The objects and advantages of the invention will be realized and
attained by means of the elements and combinations particularly
pointed out in the appended claims.
To achieve the objects and in accordance with the purpose of the
invention, the invention comprises a step-and-scan exposure method
in which patterns on a mask are transferred to shot areas on a
photosensitive substrate by a series of scanning exposures. The
method includes the steps of disposing a first shot area under a
projection optical system and a first pattern above the projection
optical system, exposing the first pattern onto the first shot area
through the projection optical system, and moving the substrate
from a first position where the exposure of the first pattern onto
the first shot area has finished to a second position where the
exposure of a second pattern onto a second shot area is to start,
and synchronously moving the mask from a third position where
exposure of the first pattern onto the first shot area has finished
to a fourth position where exposure of the second pattern onto the
second shot area is to start. An acceleration of the substrate
during movement from the first position to the second position and
an acceleration of the mask during movement from the third position
to the fourth position continually have absolute values greater
than zero.
According to another aspect, the invention comprises a
step-and-scan exposure method in which patterns on a mask are
transferred to shot areas on a photosensitive substrate by a series
of scanning exposures. The method includes the steps of disposing a
first shot area under a projection optical system, exposing a first
pattern onto the first shot area through the projection optical
system, and moving the substrate from a first position where the
exposure of the first pattern onto the first shot area has finished
to a second position where the exposure of a second pattern onto a
second shot area is to start. An acceleration of the substrate
during movement from the first position to the second position
continually has an absolute value greater than zero.
According to a further aspect, the invention comprises a
step-and-scan exposure method in which patterns on a mask are
transferred to shot areas on a photosensitive substrate by a series
of scanning exposures. The method includes the steps of disposing a
first pattern above a projection optical system, exposing the first
pattern onto a first shot area through the projection optical
system, and moving the mask from a first position where the
exposure of the first pattern has finished to a second position
where the exposure of a second pattern onto a second shot area is
to start. An acceleration of the mask during movement from the
first position to the second position continually has an absolute
value greater than zero.
It is to be understood that the foregoing general description and
the following detailed description are exemplary and explanatory
only and are not restrictive of the invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings are included to provide a further
understanding of the invention and are incorporated in and
constitute part of the specification, illustrate preferred
embodiments of the invention, and, together with a description,
serve to explain the principles of the invention.
FIG. 1 is a schematic diagram of an embodiment of a projection
exposure apparatus for use in a step-and-scan method according to
the present invention;
FIG. 2 is a perspective view of a portion of the projection
exposure apparatus of FIG. 1;
FIG. 3 is a velocity, acceleration, and jerk profile of a wafer
stage or a reticle stage during a conventional scanning
exposure;
FIG. 4 is a velocity, acceleration, and jerk profile of a wafer
stage or a reticle stage during a scanning exposure according to a
first embodiment of a step-and-scan method according to the present
invention;
FIG. 5 is a velocity, acceleration, and jerk profile of a wafer
stage or a reticle stage during a scanning exposure according to a
second embodiment of a step-and-scan method according to the
present invention;
FIG. 6 is a schematic diagram of an embodiment of a control system
for use in a step-and-scan method according to the present
invention; and
FIG. 7 is a feedback loop for a reticle stage according to the
control system of FIG. 6.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference will be made in detail to the present preferred
embodiments of the invention, examples of which are illustrated in
the accompanying drawings. Like reference numerals refer to like
parts in the various figures of the drawings.
Apparatus and methods consistent with the invention are directed
toward performing operations involving a series of relative
position changes between a substrate and a system. The operation
incorporates a single, continuous deceleration and acceleration
step during a change in direction between operations.
One embodiment of the invention is directed to a scanning exposure
of a step-and-scan method. The scanning exposure incorporates a
single, continuous deceleration and acceleration step during the
change in direction of a wafer stage or reticle stage between
individual scans of a wafer shot area. This single step increases
wafer throughput without adversely affecting the dynamics of wafer
or reticle stage motion or the velocity profiles of the stages
during the scan.
Various conventional projection exposure apparatuses may be used in
connection with the step-and-scan method according to the present
invention. The structure of one such projection exposure apparatus
is shown and described in U.S. Pat. No. 5,617,182, the complete
disclosure of which is incorporated by reference herein. The
projection exposure apparatus described in that patent will be used
for illustrative purposes. It is to be understood that the
step-and-scan method according to the present invention may be used
with various other projection exposure apparatuses known in the
art.
FIGS. 1 and 2 show the projection exposure apparatus described in
U.S. Pat. No. 5,617,182. The general structure and operation of
that conventional apparatus will be described below, followed by a
more detailed description of the step-and-scan method according to
the present invention.
In FIG. 1, light from a light source 1 illuminates a reticle R with
uniform illuminance via an illumination optical system. The optical
system includes a shaping optical system 2, a fly eye lens 3, a
condenser lens 4, a fixed field stop 5, drive section 6A and 6B, a
movable blind 7, and a relay lens system 8. The image of a circuit
pattern of the reticle R within a rectangular slit-like
illumination area 21 projects onto a wafer W via a projection
optical system 13. The light source 1 may be any suitable light
source known in the art, including the various light sources
disclosed in U.S. Pat. No. 5,617,182, and may be controlled by any
suitable means known in the art, including those described in that
patent.
With further reference to FIG. 1, the diameter of the light flux
from light source 1 is set to a predetermined value by means of
shaping optical system 2. The light from shaping optical system 2
reaches fly eye lens 3. A plurality of secondary light sources are
formed on the exit surface of fly eye lens 3 and the light from the
secondary light sources is condensed by condenser lens 4 to reach
movable blind (variable field stop) 7 via fixed field stop 5.
A rectangular slit-like opening is formed in field stop 5. The
light passed through field stop 5 becomes a light flux having a
rectangular slit-like cross section and enters relay lens system 8.
Relay lens system 8 is a lens system for making movable blind 7 and
the pattern surface of reticle R conjugate to each other. Field
stop 5 is disposed in a vicinity of movable blind 7. Movable blind
7 has a plurality of movable blades by which a rectangular opening
is formed. For example, movable blind 7 may include two blades
(light-shielding plates) 7A and 7B for defining the width of the
rectangular opening in a scanning direction (X direction) and two
blades (not shown) for defining the width of the rectangular
opening in a non-scanning direction (Y direction) perpendicular to
the scanning direction. Blades 7A and 7B for defining the width in
the scanning direction are supported so as to be driven separately
in the scanning direction by the respective drive sections 6A and
6B, and the blades for defining the width in the non-scanning
direction are supported so as to be driven separately. Within
slit-like illumination area 21 on reticle R set by field stop 5,
only a desired area set by movable blind 7 is illuminated with the
light from light source 1. That is, movable blind 7 varies the
widths of illumination area 21 in the respective scanning and
non-scanning directions. Relay lens system 8 is a both-side
telecentric optical system, and telecentric characteristics are
maintained in slit-like illumination area 21 on reticle R.
Reticle R is disposed on a reticle stage 9 and the image of the
circuit pattern within slit-like illumination area 21 on reticle R
and the area limited by movable blind 7 is projected to wafer W via
projection optical system 13. An area (projection area of the
circuit pattern) on wafer W conjugate to slit-like illumination
area 21 is a slit-like exposure area 22. Also, within a
two-dimensional plane perpendicular to the optical axis of
projection optical system 13, the scanning direction of reticle R
with respect to slit-like illumination area 21 is a +X direction
(or -X direction) and a direction parallel to the optical axis of
projection optical systems 13 is determined as a Z direction.
Reticle stage 9 is driven by a drive section 10. At the time of the
scanning exposure, reticle R is scanned (constant movement) in the
scanning direction (+X direction or -X direction). In parallel with
this scanning operation, a control section 11 controls operations
of the blinds 7A and 7B as well as drive sections thereof for the
non-scanning direction. Drive section 10 and control section 11 are
controlled by a main control system 12 for controlling the whole
operation of the apparatus.
Wafer W is disposed on a wafer stage 14. Wafer stage 14 is an XY
stage for positioning wafer W in a plane perpendicular to the
optical axis of projection optical system 13 and scanning (constant
movement) wafer W in the .+-.X direction and a Z stage for
positioning the wafer W in the Z direction. Main control system 12
controls positioning and scanning operations of wafer stage 14 via
a drive section 15.
As shown in FIG. 2, when transferring the image of the pattern on
reticle R to each shot area on wafer W, reticle R is scanned at a
speed VR in the -X direction (or +X direction) with respect to
slit-like illumination area 21. Also, the magnification of
projection optical system 13 is set to .beta., which corresponds to
relative size of the reticle pattern and the corresponding shot
area. In synchronism with the scanning of reticle R, wafer W is
scanned at a speed Vw (=.beta.XV.sub.R) in the +X direction (or -X
direction) with respect to the slit-like exposure area 22. Thereby,
the image of the circuit pattern of reticle R is transferred to the
shot area SA on wafer W.
Main control system 12 controls the exposure sequence. The
arrangement of the image pattern of reticle R is first input via an
input device 16, such as a keyboard, into a memory 17. Main control
system 12 then reads the pattern information from memory 17 prior
to determining the exposure sequence. In addition, the arrangement
of shot areas on wafer W can be obtained by detecting positions of
several alignment marks provided on each shot area and performing
statistical calculation of these positions with highly precise
position sensors. The data defining the arrangement of shot areas
may also be stored in memory 17. A more detailed description of the
operation of the control system will be provided further herein in
connection with FIGS. 6 and 7.
A conventional scanning exposure process of a step-and-scan system
typically includes six discrete process steps to transfer the image
of the pattern on the reticle to two shot areas on the wafer. FIG.
3 shows the velocity, acceleration, and jerk (rate of change of
acceleration) profiles of a wafer stage and a reticle stage during
these six steps. The steps include: (1) acceleration of the wafer
and reticle stages to a positive scanning velocity during time
period T1; (2) scanning of a first shot area of the wafer at
constant velocity in the +X direction during a time period T2; (3)
deceleration of the wafer and reticle stages to zero velocity
during a time period T3; (4) acceleration of the wafer and reticle
stages to a negative scanning velocity during a time period T4; (5)
scanning of a second shot area of the wafer at constant velocity in
the -X direction during a time period T5; and (6) deceleration of
the wafer and reticle stages to zero velocity during a time period
T6. These six steps are repeated until the entire reticle image
pattern has been transferred onto all shot areas of the wafer.
During process steps 3 and 4, the wafer and reticle are stepped in
the Y direction so that the scanning during step 5 is of the second
shot area. In addition, conventional process steps 3 and 4 are
discrete, separate steps that occur in sequence. Between these two
steps, the values of the accelerations of the wafer stage and the
reticle stage reach zero. Similarly, during process step 6 and its
subsequent process step 1, the wafer and reticle are stepped in the
Y direction so that the scanning during step 2 is of a subsequent
shot area. Once again, conventional process steps 6 and 1 are
discrete, separate steps that occur in sequence. Between these two
steps, the values of the accelerations of the wafer stage and the
reticle stage reach zero.
The velocity, acceleration, and jerk profiles shown in FIG. 3 are
similar for both the wafer and reticle stages, with the exception
that the reticle stage requires a higher magnitude of velocity due
to the relative sizes of the reticle image pattern and the wafer
shot areas, as discussed earlier. For this reason, the peak
accelerations for the reticle stage and the magnitude of jerk will
be higher for the reticle stage as opposed to the wafer stage. It
is also to be understood that the acceleration profile has been
simplified for ease of demonstration. During actual scanning, the
acceleration profile is somewhat more complicated than the
triangular acceleration profile shown.
As described earlier, no scanning occurs during the time between
scans. During this time period (represented by T3+T4 and T6+T1),
the wafer and reticle stages are stepped in the Y direction, and
the stages are decelerated to zero velocity and then accelerated in
the opposite direction to a constant scanning velocity. The
inefficiency represented by the time periods T3+T4 and T6+T1
increases the total time to manufacture a chip on a wafer and
thereby limits the throughput of wafers in a production
process.
This inefficiency is minimized according to the present invention
by incorporating a single, continuous deceleration and acceleration
step in place of the two discrete, back-to-back deceleration and
acceleration steps between scans (i.e. the steps during which a
change in direction occurs and the wafer and/or reticle stage is
stepped). For example, FIG. 4 shows the velocity, acceleration, and
jerk profiles of a reticle stage or a wafer stage during a scanning
exposure according to a first embodiment of a step-and-scan method
and system of the present invention. Certain process steps of the
scanning exposure of this embodiment are the same as the process
steps of the conventional scanning exposure profiled in FIG. 3 and
described above. For example, scan steps 2 and 5 (corresponding to
time periods T2 and T5 respectively) are the same for the inventive
scanning exposure profiled in FIG. 4 and the conventional scanning
exposure profiled in FIG. 3. In addition, the initial acceleration
to scan a first shot area of a wafer and the final deceleration
after scanning the last shot area of that wafer are the same as in
a conventional scanning exposure method.
However, between scans, the step-and-scan method profiled in FIG. 4
includes a single, continuous deceleration and acceleration process
step. That single step takes the wafer or reticle stage from the
constant scanning stage velocity in one direction to the constant
scanning stage velocity in the opposite direction. In addition,
that single step is characterized in that the acceleration of the
wafer or reticle stage never reaches a value of zero. In other
words, the acceleration continually has an absolute value greater
than zero.
For example, between the end of scanning period T2 and the
beginning of scanning period T5, a single, continuous method step
decelerates the wafer or reticle stage to zero velocity and
accelerates the stage to the constant negative scanning velocity.
This occurs during time period T7. The acceleration never reaches a
value of zero during time period T7. Similarly, between the end of
scanning period T5 and the beginning of a subsequent scanning
period, a single, continuous method step decelerates the wafer or
reticle stage to zero velocity and accelerates the stage to the
constant positive velocity for scanning a subsequent shot area.
The acceleration profile shown in the FIG. 4 embodiment has the
same peak or magnitude of acceleration as the conventional profile
shown in FIG. 3, but has a trapezoidal shape. Such acceleration
retains the same magnitude of jerk and results in a velocity
profile during the scanning steps (T2 and T5) that is identical to
the conventional velocity profile. Thus, the dynamics of stage
motion are not affected adversely by the single, continuous
acceleration during time between scans, as compared to the two
discrete steps of conventional step-and-scan systems.
However, because the constant scanning velocity during time period
T2 changes to the constant scanning velocity during time period T5
at a much faster rate, the velocity profile between scans differs
from the conventional profile. This results in a significant
reduction in the time to scan and expose a shot area or chip on the
wafer. This time reduction, in turn, results in an increase in
wafer throughput.
FIG. 5 shows the velocity, acceleration, and jerk profiles of a
reticle stage or a wafer stage during a scanning exposure according
to a second embodiment of a step-and-scan method and system of the
present invention. As in the FIG. 4 embodiment, certain process
steps of the scanning exposure of this second embodiment are the
same as the process steps of the conventional scanning exposure
profiled in FIG. 3. Once again, scan steps 2 and 5 (corresponding
to time periods T2 and T5, respectively) are the same for the
inventive scanning exposure profiled in FIG. 5 and the scanning
exposures profiled in FIGS. 3 and 4. In addition, the initial
acceleration to scan a first shot area of a wafer and the final
deceleration after scanning the last shot area of that wafer are
the same.
However, between scans, the step-and-scan method profiled in FIG. 5
includes a single, continuous deceleration and acceleration process
step. That single step takes the wafer or reticle stage from the
constant scanning stage velocity in one direction to the constant
scanning stage velocity in the opposite direction. In addition,
that single step is characterized in that the acceleration of the
wafer or reticle stage never reaches a value of zero. In other
words, the acceleration continually has an absolute value greater
than zero.
For example, between the end of scanning period T2 and the
beginning of scanning period T5, a single, continuous method step
decelerates the wafer or reticle stage to zero velocity and
accelerates the stage to the constant negative scanning velocity.
This occurs during time period T8. The acceleration never reaches a
value of zero during time period T8. Similarly, between the end of
scanning period T5 and the beginning of a subsequent scanning
period, a single, continuous method step decelerates the wafer or
reticle stage to zero velocity and accelerates the stage to the
constant positive velocity for scanning a subsequent shot area.
Unlike the FIG. 4 embodiment, the acceleration profile shown in the
FIG. 5 embodiment has a higher peak or magnitude of acceleration.
However, the deceleration and acceleration during time period T8
occurs at the same rate of change of acceleration (i.e. magnitude
of jerk) as the profiles of FIGS. 3 and 4. Such acceleration
retains the same magnitude of jerk and results in a velocity
profile during the scanning steps (T2 and T5) that is identical to
the conventional velocity profile. Thus, the dynamics of stage
motion are not affected adversely by the single, continuous
acceleration between scans, as compared to the two discrete steps
of conventional step-and-scan systems.
Like the FIG. 4 embodiment, however, because the constant scanning
velocity during time period T2 changes to the constant scanning
velocity during time period T5 at a much faster rate, the velocity
profile between scans differs from the conventional profile. This
results in a significant reduction in the time to scan and expose a
shot area or chip on the wafer. The higher peak deceleration
profiled in FIG. 5 reduces that time even more than the time
required in the first embodiment.
The first and second embodiments of a step-and-scan method and
system according to the present invention represent presently
preferred embodiments. Other step-and-scan methods and systems
incorporating single, continuous acceleration profiles during the
change in direction of scanning are within the scope of the
invention. For example, 1) Multiple sub fields on a single reticle
to expose multiple shot areas. 2) Direct write EB system with no
reticle but where water is scanned. 3) Inspection system where
nothing is being exposed.
Main control system 12 must be programmed accordingly to implement
the step-and-scan method according to the present invention into a
projection exposure apparatus, such as the apparatus shown in FIG.
1. Main control section 12 controls the positioning of the reticle
and wafer stages. All other aspects of a conventional apparatus may
remain the same.
For example, the desired trajectory, or positions, that the wafer
and/or reticle need to follow during the entire scanning exposure
process may be input into memory 17 via input device (keyboard) 16.
Main control system 12 includes software to control the movement of
the reticle and wafer stages according to the desired velocity,
acceleration, and jerk profiles. Such software may be developed by
one skilled in the art according to known programming methods.
An appropriate feedback loop would determine the current position
of the wafer, for example, and send that information to main
control system 12. Control system 12 would then determine the
desired position of the wafer from memory 17. Then, according to
the profiles programmed into main control system 12, control system
12 would cause drive section 15 to move the wafer stage so as to
correctly position the wafer. Similar feedback loops for
controlling projection exposure apparatuses are well known in the
art.
For example, FIGS. 6 and 7 schematically show a more detailed
description of a feedback loop for controlling a projection
exposure apparatus according to the present invention. As shown in
FIG. 6, a microprocessor controller 120 (part of the main control
system 12) receives feedback signals from reticle stage 9 and wafer
stage 14. Reticle stage 9 includes a coarse stage 110 and a fine
stage 116 for fine position adjustments of reticle stage 9. The
feedback signals received by controller 120 indicate the actual
position of wafer stage 14, coarse stage 110, and fine stage 116.
Controller 120 includes software to control the movement of reticle
stage 9 and wafer stage 14 according to the desired velocity,
acceleration, and jerk profiles. Based on the feedback position
signals, the desired position of the reticle and wafer stages, and
the velocity, acceleration, and jerk profiles, controller 120 sends
signals to various amplifiers to drive wafer stage 14 and reticle
stage 9. Servo amplifiers 122 and 124 drive wafer stage 14 and
reticle coarse stage 110 respectively. A PZT amplifier 118 drives a
PZT 117 for fine adjustments of reticle fine stage 116.
FIG. 7 shows a feedback loop for controlling the position of
reticle fine stage 116. It is to be understood that the feedback
loops for controlling coarse stage 110 and wafer stage 14 are
similar. A trajectory signal 115 indicating the desired stage
positions is input into a memory. Trajectory signal 115 includes
the desired position from the profiles in FIG. 3, 4, or 5.
Trajectory signal 115 is fed to controller 120. At the same time, a
signal representing the actual position of fine stage 116 is fed to
controller 120. Controller 120 determines an error or difference
between the desired position indicated by trajectory signal 115 and
the actual position. Then, controller 120 sends a signal to
amplifier 118 to actuate PZT 117 and fine stage 116 to move the
reticle to the desired position. A feedforward controller 126 may
also be incorporated into FIG. 7, as shown in broken line.
The control system shown in FIGS. 6 and 7 represents one embodiment
of a control system that may be used to implement the step-and-scan
method according to the present invention. Other control systems
known in the art for controlling a projection exposure apparatus
may be used without departing from scope of this invention. For
example, controller 120 may be a PID filter, a lead-lag filter, or
other type of filter.
Furthermore, although the invention has been described in terms of
a step-and-scan exposure apparatus and method, the principles
described herein may be applied in any positioning apparatus and
method.
When using a linear motor for the wafer stage or the reticle stage
(see U.S. Pat. No. 5,623,853 or U.S. Pat. No. 5,528,118), either an
air-floating model that employs air bearings or a magnetic floating
model that employs Lorentz's force or reactance force can be used.
The stage can either be a type that moves along a guide or a type
that has no guide (guideless).
A plane motor that drives the stage using electromagnetic force by
using a magnet unit having magnets sited two-dimensionally opposite
an armature unit in which a coil is sited two-dimensionally. If so,
either the magnet unit or armature unit can be connected to the
stage, and the other can be installed on the moving side of the
stage.
The reactive force produced by the movement of the wafer stage may
be mechanically displaced to the bed (the ground) using the frame
materials, as described in patent application H8 [1996]-166475
(U.S. Pat. No. 5,528,118).
The reactive force produced by the movement of the reticle stage
may be mechanically displaced to the bed (the ground) using the
frame materials, as described in patent application H8
[1996]-330224 (U.S. Pat. No. 5,874,820).
It will be apparent to those skilled in the art that various
modifications and variations can be made to the exposure methods of
the present invention without departing from the scope or spirit of
the invention. Thus, it is intended that the present invention
cover the modifications and variations of this invention provided
they come within the scope of the appended claims and their
equivalents.
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